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Avalanche Forecast

Archived

Apr 21st, 2017–Apr 22nd, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Glacier.

It's been days since we've had an overnight crust recovery. If the sun comes out full force today as forecast, it will rapidly destabilize the snowpack and will increase the likelihood of cornice failures.

Weather Forecast

Today we will get  increasing sun and freezing levels to 2100m. Winds will be light and won't help to cool temps. Freezing levels should drop overnight providing an overnight recovery. Sat we will see increasing cloud with light precip, and freezing levels to 2200m. Sun will be a cloudy with sunny breaks, some flurries, and freezing levels at 1900

Snowpack Summary

Below treeline there hasn't been an overnight recovery several days, with wet snow overlying and bonding poorly to a crust. Yesterday moist, mashed-potato like snow was reported to 2400m on even N aspects. It rained to at least 1900m, with ~4mm of rain changing to snow overnight. At ridgetop moderate S'ly winds will have loaded lee slopes.

Avalanche Summary

Several naturally triggered avalanches to size 2.5 were observed along the highway corridor. They were all loose, wet avalanches. A few avalanches gouged to ground once they reached the weak, isothermal snow at low elevations. Skiers have reported the top 20cm is easily triggered below treeline, with wet snow running on the crust below.

Confidence

Timing or intensity of solar radiation is uncertain

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.